Recovery of alkyllead



July 4, 1950 H. J. MADDEN RECOVERY OF ALKYLLEAD Filed NOV. 20, 1948 ACTUAL EFFECTIVENESS OF FERRIC CHLORIDE m C 0 E m T M L w m w T O. H T M m w 0 D O s m. W O. w v v ,w O v 4 u O. F l|ll l,l'l lll llllll ky o o. w 0 a 0 0 O 0 0 O y 0 V .0 00 9 8 7 6 5 .4 3 2 T I CONCENTRATION OF IRON-WEIGHT PERCENT BASED ON WEIGHT OF LEAD PRESENT INVENTQR. HAROLD MADDEN Patented July 4, 1950 RECOVERY OF 'ALKYLLEAD Harold J. Madden, Baton Rouge, La., assignor to Ethyl Corporation, New York, N. Y., a corpora.-

tion of Delaware Application November 20, 1948, Serial No. 61,214

12 Claims.

This invention relates to the recovery of alkyllead compounds from the reaction products accompanying their synthesis. More specifically it relates to an improved method of steam distilling an alkyllead compound in the presence of other reaction products formed during its manufacture.

In the manufacture of tetraethyllead, a comminuted alloy of sodium and lead is reacted with ethyl chloride. The lead content of the alloy is in substantial excess of the quantity consumed for the tetraethyllead formation, so that the products of the reaction include excess metallic lead, as well as the tetraethyllead formed. The reaction products also include considerable quantitles of sodium chloride, plus minor quantities of unused sodium. This mixture of reaction products is usually referred to as reaction mass.

Steam distillationis used to recover the tetraethyllead product from the reaction mass. The reaction mass is discharged into a still which is already partly full of water. The mixture is continuously agitated while steam is passed through the still. The mixture in the still, termed still sludge," tends to agglomerate forming a spongy porous mass in the shape of balls or forming a solid metallic mass. The solid metallic mass usually occurs as sheets or rings around the in-.

terior of the still. Such agglomerations cause considerable trouble such as overloading and jamming of the still agitator, making subsequent removal of the still sludge after distillation diflicult and in severe cases making it necessary to shut down the equipment so that this removal may be effected. The latter is a difficult task requiring unusual safety precautions due' to the toxic nature of thetetraethyllead.

Also the overall yields of tetraethyllead are adversely affected by such still troubles. When a tinuous problem. Many materials have been proposed and some used as additives to the still charge for prevention of agglomeration of the solids. These additives referred to as still aids, have not been suiiiciently effective as antiaggloinerants, and their use has frequently in- .2 troduced other difficulties, such as interference with the subsequent processing of the residue in the still for recovery of the lead content.

It is therefore an object of this invention to provide an improved still aid which greatly reduces the diificulties encountered during distillation due to the agglomeration of solid reaction products, another object is to obtain a better recovery of alkyllead products. A further object is to improve the safety and working conditions for the process.

These objects are attained by the use of two or more different materials which, when combined, exhibit a synergistic effect in their use as I still aids. My invention comprises conducting the steam distillation used for separating alkyllead products from reaction mass, in the presence of a dilute aqueous solution of a soluble iron salt and sodium thiosulfate. I have found that these materials, used in combination, exhibit a morethan-additive effectiveness in preventing agglomeration and in minimizing steam distillation difficulties. This makes possible greatly improved performance of the steam distillation, even when the agglomerative tendency of reaction mass solids is quite severe.

Generally, all of the iron salts are suitable for combinin with sodium thiosulfate providing that they are water soluble. Salts of both inorganic or organic acids may be used. Thus an organic salt, such as ferrous lactate, is satisfactory. Mixed or double salts are effective also, providing that one of the cations is an iron ion, for example, ferric ammonium oxalate. The valence of the iron in the salt is not important, both ferrous and ferric salts being beneficial. Ferrous sulfate is especially desirable since it is not only effective but is readily available and inexpensive. Among other beneficial soluble iron salts are ferric chloride, ferrous chloride, ferric nitrate, ferric phos-' phate and ferric sulfate.

The iron salts of my invention are beneficial over a wide concentration range, when used in conjunction with sodium thiosulf-ate. Concentration is expressed herein in terms of the iron, Fe, introduced in the iron salt, as weight per cent based on the weight of lead present in the reaction mass. The iron salt can be used in con centrations between 0.003 and 0.12 weight per cent. with a high degree of effectiveness. Conce'ntrations, above 0. 2 weight per cent usually are not required ex ept when the agglomerative tendency of the reaction mass is especially severe. For the average reaction mass concentrations be- .tween 0.003 and 0.06 are satisfactory.

3 The concentration of the sodium thiosulfate is not critical, but should be at least 0.1 per cent by weight based on the weight of the lead present in the reaction mass. Concentrations of sodium thiosulfate between 0.1 and 0.8'per cent by weight are satisfactory in most instances. Concentrations above 0.8 weight per cent are usually not. required. However where the agglomeration tendency of the reaction mass is severe higher concentrations are beneficial.

The quantity of water used in the steam still may be varied widely and good results obtained. In general the amount of water should be sufflcient to submerge fully the reaction mass at the a start of the distillation. At water solution of the still aids is preferable so that the dissolved salts will ,be in contact with all parts of the reaction mass at the start of the distillation.

To illustrate the surprising nature of the invention, an embodiment on a large scale is described. A still was charged with 3100 pounds of water, 2.5 pounds of ferric chloride added as FeClx-SHzO and 19 pounds of sodium thiosulfate added as Na2SzO3-5H2O. Then a charge of about 4500 pounds of reaction mass was introduced during agitation. The reaction mass contained about 2500 pounds of predominantly lead particles, about 1100 pounds of tetraethyllead and roughly 900 pounds of sodium chloride. The

lead particles contained a small percentage of excess sodium, which was converted to sodium hydroxide by reaction with the water in the still.

Open steam was passed through the still and the distillation continued for 90 to 120 minutes, :which was adequate for separation of the recoverable tetraethyllead. No "still trouble" was encountered in this procedure or in numerous the average effectiveness of ferric chloride alone,

, the expected effectiveness of ferric chloride with sodium thiosulfate based solely onan additive effect, and the observed effectiveness of the latter.

Line 0A shows the average efiectiveness of ferric chloride alone, within a concentration range of 0 to 0.06 per cent. For example, at a concen- :combined still aid is synergistic in nature, reference is made to the accompanying plot. This plot is based on large scale operations and shows shown by line F0, was obtained on sodium thiosulfate concentrations as iow as 0.4 weight per cent and in no case did the concentration exceed 0.8 weight per cent. Thus, shaded area HFCB represents the unpredictable and. unexpected more-than-additive benefits obtained by usin my combination of still aids.

The line FCrepresents average eifectiveness in reaction masses having a normal tendency to agglomerate. Since complete effectiveness has been obtained at low concentrations of iron with sodium" thiosulfate, the higher concentrations were not fullyv utilized. However, higher concentrations of iron, in, combination with sodium thiosulfate, are advantageous when'the reaction mass exhibits especially severe tendency toward agglomeration.

Similar surprising results were obtained with ferrous sulfate. For example, 0.06 per cent of ferrous sulfate used alone resulted in an effectiveness of about 30 per cent. However when the same concentration of ferrous sulfate was used with sodium thiosulfate in concentration between 0.6 and 0.8 per cent, the effectiveness consistently ranged between 90 and 95 per cent. In striking contrast, the effectiveness expected due to only an additiveeffect is only about 62 per cent.

Thus I have demonstrated that my still aids are outstanding in effectiveness and that a-more than an additive effect is obtained over the use of either an iron salt or sodium thiosulfate alone. My invention is not limited to a process for the recovery of tetraethyllead but it is applicable to improving the recovery by steam-'distillation of other alkylleads such as tetramethyllead, tetra propyllead, dimethyldiethyllead, and trimethylphenyllead. I

I claim: v v

1. A process of'recovering an alkyllead from the reaction products accompanying its synthesis comprising steam distilling the reaction mass in the presence of an aqueous. solution of an iron salt. and sodium thiosulfate.

2. A process of recovering an alkyllead from the reaction products accompanying its synthesis comprising steam distilling the reaction mass in the presence of an; aqueous solution of an iron salt and sodium thiosulfate, said solution containing iron in an amount equivalent to at least 0.003 per cent byiweight of the lead present in the reaction products and sodium thiosulfate in an amount equivalent to at least 0.1 per cent by weight of the lead present 'in the reaction products.

3. The process of claim 2 further defined in that the iron salt comprises a chloride of iron.

tration of 0.04 weight percent, ferric chloride alone is about 37 per cent effective. Line FC'is the observed effectiveness for varying concentrations of ferric chloride in combination with the sodium thiosulfate concentrations varying vorable concentration of 0.8 weight per cent results in an effectiveness of only 32 per cent.

Therefore line HB represents the effectiveness expected due only to an additive effect for a com- 4. The process of claim 2 further defined in that the iron salt comprises a sulfate of iron.

5. I'he process of claim 2 further defined in that the iron salt comprises a nitrate of iron.

6. A process of recovering tetraethyllead from the reaction products accompanyin its synthesis comprising steamdistilling the reaction mass in the presence of. an aqueous solution of iron salt and sodiumthiosulfate, said solution containing ,iron in anamount equivalent to 0.003 to 0.06 per bination of different concentrations of ferric sulfate, 9. per cent eifectiveness was obtained i at ferric chloride concentrations above 0.003 per cent, as shown by line FC. This is all themore f surprising because .the observed effectiveness cent by weightof the lead in' the reaction products and sodium thiosulfate in an amount equivalent to 0.1 to 0.8-per centiby weight of the lead presentin the reaction products, Y

. 7. Thep'rocess of claim-(ifurther define'dinb that the iron saltv comprises ferrous sulfate.

-a. The process of claim 6 further defined in that the iron salt comprises ferric chloride.

5 9. In the process of preparing tetraethyllead by reacting sodium-lead alloy and ethyl chloride, and recovering tetraethyllead from the products of reaction accompanying its synthesis,

the step of steam distilling tetraethyllead there- 5 from in the presence of aqueous solution containing an iron salt having an iron content in amount equivalent to from 0.003 to 0.12 per cent by weight of the lead present in the reaction products, and sodium thiosulfate in an amount equivalent to from 0.1 to 0.8 per cent by Weight of the lead present in the reaction products.

10. The process of claim 9 further defined in that the iron salt comprises a sulfate of iron.

11. The process of claim 9 further defined in that the iron salt comprises a nitrate of iron.

12. The process of claim 9 further defined in that the iron salt comprises a chloride of iron.

HAROLD J. MADDEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,645,375 Daudt Oct. 11, 1927 2,004,160 Downing June 11, 1935 2,038,703 Bake et a1. Apr. 28, 1936 2,038,704 Bake et a1. Apr. 28, 1936 FOREIGN PATENTS Number Country Date 214,221 Great Britain July 22, 1925 516,875 Great Britain Jan. 15, 1940 

1. A PROCESS OF RECOVERING AN ALKYLLEAD FROM THE REACTION PRODUCTS ACCOMPANYING ITS SYNTHESIS COMPRISING STEAM DISTILLING THE REACTION MASS IN THE PRESENCE OF AN AQUEOUS SOLUTION OF AN IRON SALT AND SODIUM THIOSULFATE. 